Constant Voltage and Constant Current Charging System for Anti-Offset Wireless Power Transmission and Its Control Method

Abstract

The present invention discloses a constant voltage and constant current charging system for anti-offset wireless power transmission and its control method. An inverter on the transmitting side, a midpoint of the first bridge arm, a primary side compensation inductor, a series capacitor of the transmitting coil, the transmitting coil, and a midpoint of the second bridge arm are connected to form a loop. One end of a first switch control capacitor module is connected between the primary side compensation inductor and the series capacitor of the transmitting coil, and the other end is connected between the transmitting coil and the midpoint of the second bridge arm; a receiving coil, which inductively couples with the transmitting coil and is connected to a rectifier bridge through a second switch control capacitor module; the rectifier bridge is connected to a battery. The present invention does not need to design a special topology structure, nor does it require an additional DC / DC converter to increase costs, and can be widely applied in fields such as electric vehicles, self-guided robots, and unmanned aerial vehicles.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a constant voltage and constant current charging system for anti-offset wireless power transmission and its control method. Background Art

[0002] Wireless Power Transfer (WPT) systems have the advantages of safety, flexibility, convenience, etc., and are widely used in fields such as electric vehicles, self-guided robots, and unmanned aerial vehicle equipment. The charging of electric vehicle batteries usually requires constant current and constant voltage output characteristics, which is beneficial to the improvement of battery life and efficient charging. However, the non-linear change of the equivalent load and the change of mutual inductance caused by misalignment during the charging process will damage the constant voltage and constant current charging of the battery. Therefore, it is a challenge for the WPT system to provide a constant and load-independent output voltage / current. Another requirement is high efficiency, which has been widely regarded as an important goal in the design of WPT systems. In recent years, control methods such as DC-DC converters and pulse frequency modulation have been used to achieve constant voltage or constant current output characteristics. However, the adjustment range of the DC-DC converter is too wide, which may lead to the loss of zero voltage switching (ZVS) and zero phase angle (ZPA) conditions, reducing the transmission efficiency of the system. In addition, the use of the pulse frequency modulation method will cause the phenomenon of frequency bifurcation, making the system unstable.

[0003] Most traditional constant voltage and constant current charging methods mainly fall into two categories: specific compensation topologies or pulse frequency modulation. Specific compensation topologies are hybrid WPT systems that combine two different output characteristic compensation topologies. These hybrid topologies require additional switches and corresponding control methods to switch output modes. Therefore, the complexity of the control scheme and the risk of circuit failures are increased. In addition, the misalignment tolerance is poor. The pulse frequency modulation method switches the constant voltage and constant current output by switching the operating frequency of the system. When the operating frequency of the system deviates too much from the optimal frequency, frequency modulation will lead to a decrease in power transmission capacity. In addition, the available frequency range is specified by the Industrial, Scientific and Medical (ISM) of the Radiocommunication Sector of the International Telecommunication Union, J2954 of the Society of Automotive Engineers (SAE), and the Qi standard of the Wireless Power Consortium (WPC), making the pulse frequency modulation have limitations. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide, in view of the deficiencies of the prior art, a constant voltage and constant current charging system for anti-offset wireless power transmission and its control method, which can realize the switching between constant voltage output and constant current output of the constant voltage and constant current charging system without additional devices.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a constant voltage and constant current charging system for anti-offset wireless power transmission, comprising:

[0006] The inverter on the transmitting side, the midpoint of the first bridge arm of the inverter, the primary-side compensation inductor L1, and the series capacitor C of the transmitting coil P , the transmitting coil L P , and the midpoint of the second bridge arm of the inverter are connected to form a loop. One end of the first switch control capacitor module is connected between the primary-side compensation inductor and the series capacitor of the transmitting coil, and the other end is connected between the transmitting coil and the midpoint of the second bridge arm;

[0007] The receiving coil is inductively coupled with the transmitting coil and is connected to the rectifier through the second switch control capacitor module; the rectifier is connected to the battery; the first switch control capacitor module and the second switch control capacitor module have the same structure; the switch capacitor module includes a first branch and a second branch, and the first branch includes a capacitor C σ , and the second branch includes two switch tubes connected in reverse series, and the first branch and the second branch are connected in parallel;

[0008] The equivalent capacitance of the first switch control capacitor module or the second switch control capacitor module The calculation formula is:

[0009]

[0010] Among them, is the control delay angle, satisfying

[0011] In the present invention, by controlling the capacitor with a switch to change the equivalent capacitance value, the switching between constant voltage output and constant current output can be realized. By continuously changing the phase-shifting control angle θ of the inverter, the charging voltage U B and the charging current I B can be adjusted. The present invention does not need to design a special topology structure, nor does it need an additional DC / DC converter to increase the cost, and can be widely applied in the fields of electric vehicles, self-guided robots, drones, etc.

[0012] As an inventive concept, the present invention also provides a control method for the constant voltage and constant current charging system of the above anti-offset wireless power transmission, which includes the following steps:

[0013] According to the formula Among them, ω is the switching angular frequency, calculate the equivalent capacitance of the first switch control capacitor module C1 and the second switch control capacitor module C S in the constant voltage charging mode. Then, based on the formula Adjust the corresponding control angles of the first switch capacitor module and the second switch capacitor module Measure the mutual inductance M0, and determine the DC input voltage U required for battery charging dc and the charging voltage U B, adjust the phase shift angle θ so that the output voltage reaches a preset constant voltage value;

[0014] According to the formula Calculate the C1 and C S The capacitance value is based on the formula Adjust the control angles of the first switch capacitor module and the second switch capacitor module According to the constant current charging current size I required by the battery B , adjust the phase shift angle θ so that the output voltage reaches the preset constant current value, M is the mutual inductance in the constant current output mode;

[0015] When the mutual inductance coil is offset, the mutual inductance M1 is measured at this time, and the phase shift angle θ is adjusted to restore the output voltage to a preset constant voltage value.

[0016] In the present invention, in the constant voltage charging mode, the voltage gain G CV for: Among them, U O is the output voltage of the constant voltage and constant current charging system, R O is the equivalent input resistance on the rectifier side. R B The size of the battery equivalent load resistance, U1 is the output voltage of the transmitter-side inverter, R S is the parasitic resistance of the receiving coil.

[0017] The method according to claim 3 is characterized in that, in the constant current output mode, the output current is: I O Output current for constant voltage constant current charging system The effective value size, U dc is the DC voltage source output voltage.

[0018] Compared with the prior art, the present invention has the following beneficial effects: the present invention only controls the angle by a capacitor. Adjust the equivalent capacitance of the switch control capacitor at the transmitting and receiving ends to achieve the switching between constant voltage output and constant current output, meet the battery constant voltage and constant current charging requirements, protect battery safety and extend battery life. The corresponding voltage and current can be adjusted by the inverter phase shift angle. This method avoids the frequency bifurcation problem that may be caused by switching system frequency and can be widely used in electric vehicles, smart phones, medical and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a structural diagram of the LCC-S compensation topology WPT system according to an embodiment of the present invention;

[0020] Figure 2 This is a diagram of an equivalent circuit structure of an LCC-S compensation topology according to an embodiment of the present invention;

[0021] Figure 3 This is the schematic diagram of the method in the embodiment of the present invention;

[0022] Figure 4 This is the flowchart of the constant voltage and constant current output characteristics in the embodiment of the present invention;

[0023] Figure 5 This is the constant voltage and constant current output diagram of the system in the embodiment of the present invention; (a) Constant voltage mode: θ = 80.64., V dc = 100V; (b) Constant current mode: θ = 180., V dc = 100V. Detailed implementation manners

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] Figure 1 For a magnetic - coupled wireless power transfer system based on the LCC - S topological structure with a switched - controlled capacitor, the entire transfer system includes an inverter circuit, a resonant circuit, and a rectifier output circuit. After the LCC resonant topology, energy flows from the primary - side coil to the secondary - side through magnetic coupling. Then the system outputs energy through the rectifier circuit. U dc is the output voltage of the DC voltage source, which is used to drive the primary - side high - frequency bridge inverter circuit to generate a high - frequency square - wave voltage. U1 is the output voltage of the inverter, and θ is the inverter phase - shift control angle. S1 - S4 are the inverter switching tubes on the transmitting side. C1 and C S is a switched - capacitor module with an adjustable equivalent capacitance value. L1, C P is the primary - side compensation inductor and the series capacitor of the transmitting coil. L P and L S are the equivalent inductances of the transmitting coil and the receiving coil. M is the mutual inductance between the transmitting coil and the receiving coil. R P and R S are the parasitic resistances of the transmitting coil and the receiving coil respectively, and R O is the equivalent input resistance on the rectifier side. R B is the magnitude of the equivalent load resistance of the battery. C S is the secondary - side compensation capacitor.

[0026] As Figure 1 shown, in the embodiment of the present invention, the switched - capacitor modules C1 and C Shas the same structure. Taking the switched-capacitor module C1 as an example, it includes: a first branch including a capacitor C σ ; a second branch including two series-connected switching tubes Sp1 and Sp2, each switching tube being connected in parallel with a diode; the first branch and the second branch are connected in parallel.

[0027] Figure 2 is the LCC-S equivalent circuit model, and the impedances of each part of the system are expressed as

[0028]

[0029] where ω is the operating angular frequency of the wireless power transfer system. For simplicity of analysis, the fundamental wave approximation is adopted, and only the fundamental wave component is considered. And the effective value of the fundamental wave U1 of the inverter output voltage is

[0030]

[0031] Kirchhoff's voltage equations (KVL) are written at the transmitting side and the receiving side:

[0032]

[0033] where, is the AC output current of the inverter, and are the currents passing through the transmitting coil and the receiving coil respectively. When the resonance condition of the following formula is satisfied through model derivation, the system can operate at a constant voltage output:

[0034]

[0035] It is characterized in that a constant voltage output is achieved by designing the system to operate in a constant voltage mode. The frequency is the operating frequency of the system, and the voltage gain G CV is:

[0036]

[0037] where U O is the magnitude of the system output voltage, and R O is the magnitude of the load resistance. The simplification in (5) is due to the fact that the parasitic resistance R S is very small. It can be seen from the expression of the voltage gain that: when the mutual inductance remains unchanged, the voltage gain G CV is constant. Since the inverter output voltage U1 is constant, the constant voltage gain G CV represents the constant output voltage U O is constant, and the system can achieve a constant voltage output. In addition, the input impedance Z in of the system can be derived as

[0038]

[0039] Obviously, the input impedance of the LCC-S system has no imaginary part, the power factor is the unity power factor, and zero phase angle output can be achieved. The invented constant voltage and constant current system can maintain high transmission efficiency.

[0040] The described design is based on the adjustable switched capacitor control strategy for constant current output. It is characterized in that the circuit parameters of the original constant voltage output cannot guarantee its constant current output, and it is necessary to adjust the switched capacitor to change the equivalent capacitance parameter. Under constant current output, it should satisfy

[0041]

[0042] Based on Equation (7), under constant current output, the switched capacitors C1 and C S The new equivalent capacitance value parameter should be adjusted to

[0043]

[0044] Based on (8), the transconductance gain G CC can be calculated as

[0045]

[0046] Combining (2) and (9), the magnitude of the output current in the constant current mode is

[0047]

[0048] I O is the effective value of the system output current Under the condition that the inverse mutual inductance and the input voltage remain unchanged, the output current remains constant, and its magnitude can be adjusted by θ. Therefore, by changing the equivalent capacitance value through the switched capacitor, the switching between constant voltage output and constant current output can be achieved to meet the battery charging requirements. The specific calculation of the equivalent capacitance of the switched capacitor is

[0049]

[0050] where C σ is the parallel capacitance of the switched capacitor, is the control delay angle, satisfying Changing the control angle value can further adjust the equivalent capacitance, so as to achieve the switching between constant voltage output and constant current output and adapt to the battery charging requirements.

[0051] The constant voltage and constant current method specifically includes the following steps:

[0052] Step 1: According to Equation (4), design the system parameters L1, C1, L P , CP , L S , C S and the system switching angular frequency ω, the mutual inductance of the measuring coil is denoted as M0. At this time, the system operates in the constant voltage mode. Determine the DC input voltage required for battery charging under constant voltage output and the charging voltage U dc and U B , adjust the phase shift angle θ to make the output voltage reach the preset constant voltage value U B , adjusting the phase shift angle θ is achieved by changing the modulation of the MOS transistor gate PWM signal in the inverter (Lu Jianhua, Hao Kaimin, Yang Wenqi, etc. Two methods for generating phase-shifted PWM based on TMS320F2812 [J]. Journal of Naval Aeronautical and Astronautical University, 2020, 35(06): 478-482.);

[0053] Step 2: According to equation (8), calculate the capacitance values of C1 and C S under constant current output, and adjust the control angles of the switching control capacitors C1 and C S correspondingly based on equation (11) According to the magnitude of the constant current charging current I B required by the battery, adjust the phase shift angle θ (Lu Jianhua, Hao Kaimin, Yang Wenqi, etc. Two methods for generating phase-shifted PWM based on TMS320F2812 [J]. Journal of Naval Aeronautical and Astronautical University, 2020, 35(06): 478-482.), so that the output voltage reaches the preset constant current value I B ;

[0054] Step 3: When the coil is offset, measure the mutual inductance at this time and denote it as M1. Adjust the phase shift angle θ to make the output voltage return to the preset constant voltage value U B ;

[0055] Step 4: Adjust the phase shift angle θ to make the output current return to the preset constant current value I B .

[0056] Figure 5 is the system constant voltage and constant current output diagram. In the constant voltage mode, when the equivalent load resistance R B of the battery increases from 50Ω to 60Ω, the output voltage represented by the cyan waveform remains at about 84V, maintaining constant voltage output. At this time, θ = 80.64. In the constant current mode, when the equivalent load resistance R B of the battery increases from 20Ω to 40Ω, the output voltage represented by the blue waveform remains at about 4A, maintaining constant current output. At this time, θ = 180..

[0057] Although the preferred embodiments of the present application have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present application.

[0058] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A constant voltage and constant current charging system for anti-deviation wireless power transmission, characterized in that: include: The transmitting end and the receiving end; wherein the transmitting end includes an inverter, a midpoint of the first bridge arm of the inverter, a primary side compensation inductor L1, and a transmitting coil series capacitor C P , transmitting coil L P , the midpoint of the second bridge arm of the inverter is connected to form a loop, one end of the first switch control capacitor module C1 is connected between the primary side compensation inductor and the transmitting coil series capacitor, and the other end is connected between the transmitting coil and the midpoint of the second bridge arm; The receiving end includes a receiving coil, the receiving coil and the transmitting coil are mutually inductive, and the capacitor module C is controlled by a second switch. S connected to a rectifier; the rectifier is connected to a battery; The first switch-controlled capacitor module and the second switch-controlled capacitor module have the same structure; the first switch-controlled capacitor module includes a first branch and a second branch, the first branch includes a capacitor C σ , the second branch includes two switch tubes connected in reverse series, and the first branch and the second branch are connected in parallel; The equivalent capacitance of the first switch-controlled capacitance module or the second switch-controlled capacitance module The calculation formula is: Among them, C σ is the capacitance of the first branch of the first switch-controlled capacitance module or the second switch-controlled capacitance module, To control the delay angle, satisfy 2. The constant voltage and constant current charging system for anti-deviation wireless power transmission according to claim 1, characterized in that: In the constant current mode, the capacitance values ​​C1 and C2 of the first switch-controlled capacitor module or the second switch-controlled capacitor module are S They are: Among them, ω is the switching angular frequency of the constant voltage and constant current charging system, L1 is the primary side compensation inductance value, L S is the equivalent inductance of the receiving coil, and M is the mutual inductance between the transmitting coil and the receiving coil.

3. The constant voltage and constant current charging system for anti-deviation wireless power transmission according to claim 1, characterized in that: In the constant voltage mode, the capacitance values ​​C1 and C2 of the first switch-controlled capacitor module or the second switch-controlled capacitor module are S They are: ω is the switching angular frequency of the constant voltage and constant current charging system, L1 is the primary side compensation inductance value, L S is the equivalent inductance of the receiving coil.

4. A control method for a constant voltage and constant current charging system for anti-offset wireless power transmission according to claim 2 or 3, characterized in that: The following steps are involved: According to the formula Calculate the first switch-controlled capacitor module C1 and the second switch-controlled capacitor module C in the constant voltage charging mode. S The equivalent capacitance of the battery is measured, the mutual inductance M0 is measured, and the DC input voltage U required for battery charging is determined dc and charging voltage U B , adjust the phase shift angle θ to make the output voltage reach the preset constant voltage value; ω is the switching angular frequency of the constant voltage and constant current charging system; According to the formula Calculate the C1 and C S The equivalent capacitance size is based on the formula Adjust the control angles of the first switch-controlled capacitor module and the second switch-controlled capacitor module According to the constant current charging current size I required by the battery B , adjust the phase shift angle θ so that the output voltage reaches the preset constant current value, M is the mutual inductance in the constant current output mode; When the mutual inductance coil is offset, the mutual inductance M1 is measured at this time, and the phase shift angle θ is adjusted to restore the output voltage to a preset constant voltage value.

5. The method according to claim 4, characterized in that In constant voltage charging mode, the voltage gain G CV for: Among them, U O is the output voltage of the constant voltage and constant current charging system, R O is the equivalent input resistance on the rectifier side, R B is the size of the battery equivalent load resistance, U1 is the output voltage of the transmitter-side inverter, R S is the parasitic resistance of the receiving coil.

6. The method according to claim 4, characterized in that In constant current output mode, the output current is: I O Output current for constant voltage constant current charging system The effective value size, U dc is the DC voltage source output voltage.

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